4-Acetyl-2,3,4,5-4H-benzo[1,4]diazepine (represented by formula A) is a pharmaceutical intermediate with biological activity, and has been applied in the preparation of tranquilization, antibiotic and anticancer drugs (J. Med. Chem. 1999, 42, 5241; J. Med. Chem. 1996, 39, 3539; Bioorg. Med. Chem. Lett., 2004, 14, 2603).

According to the literatures, in general, the compound represented by formula A is prepared by reducing 1,3,4-3H-benzo[1,4]diazepine-2,5-dione (represented by formula B) with LiAlH4 to give a key intermediate represented by formula III, and then acetylating the compound represented by formula III, which is illustrated by reaction scheme 1. This process has disadvantages in that it needs high cost raw materials and is not suitable for a large-scale commercial production, because expensive LiAlH4 was used in a very large amount in the reaction for preparing compound III from compound B, and anhydrous tetrahydrofuran which is difficult to be recovered was used as a solvent.
